Long story short: As per today, connectivity diagram in the Ring app is wrong for Golmar T-900.
I was able to open the door but I received no calls.
Solution was to connect A-6 cable to position 0 of the interphone (instead position 7)
Probably many other Goldmar schemas has same error, as the diagrams the Ring app is providing are the same for electronic & buzzer calls (in Golmar T900, position 0 is for electronic call, 7 for buzzer one)
No “Intercom” tag in the forum, so feel free to move where this corresponds better
Salud y saludos